I checked it out.
Firstly- I think it would work best on a touchscreen. Drawing circles with a mouse was a bit slow, but doable.
The other thing- I think that five minutes is a bit long. The game gets good, when there's a lot of souls at the same time, and the beginning is easy. Ramping up the difficulty faster would work well here.
It felt cool, when one drawing made multiple symbols disappear, but chance of this happening was relatively low. To have this happen more often you can consider new souls to have symbols based on those already on the screen, or not having to do symbols in order.